Posted
by
samzenpus
on Thursday November 28, 2013 @09:35PM
from the cut-them-up dept.

Zothecula writes "Originally discovered by accident in the 1980s, black silicon is silicon with a surface that has been modified to feature nanoscale spike structures which give the material very low reflectivity. Researchers have now found that these spikes can also destroy a wide range of bacteria, potentially paving the way for a new generation of antibacterial surfaces."

The silicon structures they were looking at were in the 500nm range, the dragonfly ones ~240nm. That's a huge amount of additional surface area, and on a scale where interaction with gas molecules will probably owe a vexing and deeply unhelpful amount to causes that we normally leave to the chemists, rather than idealized fluid behavior or largely ideal gas kinetic behavior...

I wish the best of luck to whoever gets to model the behavior of a mixed (mostly) nonpolar gas interacting with a dense, more or less randomly packed, array of 240nm spikes, composed of some sort of complex biological polymer arrangement, at the boundary of the (already complex enough) interaction between an insect wing and the surrounding fluid...

(If it turns out that the bugs are capable of using cell membrane potentials to selectively induce dielectric polarization of the air passing over selected parts of the wing surface, or something else verging on plain cheating, I say we back away slowly and let them take over.)

I wish the best of luck to whoever gets to model the behavior of a mixed (mostly) nonpolar gas interacting with a dense, more or less randomly packed, array of 240nm spikes, composed of some sort of complex biological polymer arrangement, at the boundary of the (already complex enough) interaction between an insect wing and the surrounding fluid.

Well, that doesn't tell us anything about bugs; but if you've got a proposal that will make wings work in a vacuum with just a tweak to surface geometry... I think we can overlook the bug issue and examine that result.

"If it turns out that the bugs are capable of using cell membrane potentials to selectively induce dielectric polarization...."

A most wonderful wicked question. I'm wondering, given what their metabolism is like, if they'd really need to flap their wings at all - or just do so for added effect, flying like a normal winged critter.

Depending on how this pans out, not only do we get nifty new knowledge about an area of which we mostly know nothing, but end up with great biocide wipes and, make it big enough,

My suspicion is that you'd need pretty alarming (by biological standards) voltages to get significant changes in the behavior of oxygen and nitrogen; and (for some vexing reason having to do with 'practicality' or such nonsense) my shoddy attempt at research was drowned out by the wealth of sources addressing the behaviors of dielectric gasses from the perspective of somebody who wants to fill his high-voltage transformer with one, so I couldn't find anything about viscosity, adsorption, etc.

Well, you got the science on me; I had just been doing so old-fart musing via still-surviving gee-whiz enthusiasm and pulled some stray bits out of my, um, odd niches of shelving in the mustier parts of brain. Just now I've come from Wikipedia and a quick half-hour of reading this and that; turns out O2 has a Van der Waals radius of 152pm. If there might be any interaction at, say, the tip of a spike and the adjacent bits of atmosphere, beats me. It's been too long since I've used any of this stuff, so c

" ... the wings of the cicada Psaltoda claripennis could shred certain types of rod-shaped bacteria... "
" ... the wings of the Diplacodes bipunctata or Wandering Percher dragonfly were even more deadly, killing both rod-shaped and spherical bacteria... "

I am very curious.

Since the structures on the WINGS of the insects, do they have some yet-to-be-discovered aero-dynamic functionality, apart from their ability to shred bacteria ?

My first thought was "I wonder how the structure changes the reflection of sound?"

Maybe the wings are deadened for sound in defense against bats. (Which would create massive selective pressure, bats are extremely efficient predators of insects.)

I could understand how even the smallest bacterial infection on an insect wing could compromise it's owner, but it seems like those structures would be everywhere, because a bacterial infection ANYWHERE can compromise it's owner. So why wouldn't the same structur

Durability of an exotic surface structure can be a problem. An example is ultra-hydrophobic coatings. (Now available at retail as Rust-Oleum NeverWet.) They really do repel liquids so thoroughly that coated surfaces can't even get muddy. But they seem to wear out quickly. There are YouTube videos showing that stuff working for ten minutes, then failing. But maybe someone will come up with an improved coating that's tougher.

I imagine that that's why those bugs are getting away with them. Nothing like being biological to get aggressive self-repair capabilities thrown in more or less for free... Pending nanites, no such luck on our end.

Marine anti-fouling coatings have similar trouble: they've tried to make less toxic ones, with specially crafted surface geometry that resists mooring by marine organisms; but the minute it starts to wear out, boom, stuff growing. Even the ones that are laced with ghastly organometallic biocides eventually leach enough to lose effectiveness and have to be stripped and re-applied.

(though, speaking of anti-fouling coatings, if microspike-structures are aerodynamic enough for insect wings and brutally biocidal, I suspect that the world's marine shipping industry would fight like dogs to give you their money if you could paint this stuff on...)

Was reading about that the other day, the nano-spikes act to break up water droplets into smaller droplets allowing them to bounce off the surface more easily. The same principle also allows the droplets to slide off the surface more easily, useful for boats and planes. Shark skin has similar nano-scale surface geometry, allowing the shark to move faster with less energy. With dragonflies it's apparently the network of ultra-fine capillaries on the wings that does the same job as the spikes.

You fight wearing out by making internal structure such that it sheds in layers which reveal new surface-like layers beneath them as they fall off. For that, you need to design connection points between layers to most probably fail (to be weakened) first. Like a bed of sharp nails connected by its fine points to another bed of nails above, and that one with another one above it... etc.

Then, I'd suggest you research some methods to deal with the increase of temperature in your car, due to the absorbtion of light in the spectral range 350–1150 nm (near infrared to near UV) - you'll need to dissipate approx 1 kW for each square meter of absorbing surface [wikipedia.org]

Wrong size scale for radar, which would require ~ 1 cm scale features (which might be difficult to combine with reasonable aerodynamic efficiency). Or, you need to specially shape your entire car --- like the crazy angular surfaces of funny-shaped stealth aircraft --- to avoid any surfaces with a direct reflection path back to the transmitter. I suppose a super-black car might confound lidar; even if it didn't, at least it would look pretty cool. Until some truck sideswipes you at night because they didn't

Happily, I read down the thread this far instead of rushing out to get a few square meters of double sided tape and a half a million dragonfly wings... thanks for saving my time and I'm pretty sure all the dragonflies that won't have to walk home would also be appreciative.

"This structure generates a mechanical bacteria killing effect which is unrelated to the chemical composition of the surface," says Professor Crawford, who is Dean of the Faculty of Life and Social Sciences at Swinburne.

Very low level abrasive... I wonder if and how that might serve as a soap.

Soap also serves as a pretty good soap. I suspect the fine size scale of these structures, on a rigid silicon backing, would't be too good at reaching into very much of the rugged mountainous topography (on a bacteria's scale) of human skin.

Even when they're not used for cleaning hands materials like this are useful for keeping surfaces cleaner to reduce germ transmission. I've read that simple brass and other copper alloys also have similar properties [copper.org] and there was a brief campaign to use it for things such as door handles in hospitals. Brass would most likely be much more economical to produce and has the added benefit of being very easy to recycle.

"It slices!, it dices! and chops and grinds for all your bacteria processing needs! No more fuss and muss! No more missing mitochondria! And all this can be yours for 4 low monthly payments of just $39.99! It's a limited offer, so get yours nooowwww!"

Well quite. The victorians used them everywhere in hospitals and so -unwittingly - created places that were for the time pretty damn clean. But then a plain old metal isn't hi-tech and 21st century gee-wiz so regardless of being cheap and effective its unlikely to be trumpeted by the kool kids and researchers with an eye on the next grant payment.